1. Field of the Invention
The present invention relates to an auto-focus camera and, more particularly, to an auto-focus mechanism therefor.
2. Description of the Prior Art
As is well known, in a conventional auto-focus camera, a focusing lens is guided in a direction parallel to a lens optical axis by a guide groove or a guide rod, and is moved along the lens optical axis by a moving member driven by a focus control motor through a multi-stage reduction gear train.
Therefore, in the structure of the auto-focus camera, since a reduction gear ratio of the linear movement of the moving member to the rotation of the focus control motor becomes very high, a large number of reduction gears must be used in order to obtain such a reduction gear ratio. In this structure, since the guide member and the moving member of the focusing lens are separated by a given distance, a mechanical play or deformation thereamong causes an extension error along the lens optical axis of the focusing lens. Since the moving direction of the moving member is not adjusted with respect to the lens optical axis, an error in the moving direction of the moving member is directly reflected in the extension error of the focusing lens. In this structure, during adjustment after camera assembly, focusing must be performed so that the position of the focusing lens is adjusted to an infinite focal point. For the purpose of focusing, a plurality of adjusting screws are arranged between the focusing lens and a lens holding frame for holding it. Since these adjusting screws are assembled, an assembly of the focusing lens is complicated, and a lubricant may be attached to the surface of the focusing lens, thus contaminating the focusing lens.
In the auto-focus camera of this type, in order to cause the optical axis of the focusing lens to coincide with the lens optical axis, a fine-adjustment means for the guide member must be arranged.
In other words, in an auto-focus mechanism of the conventional auto-focus camera, a large number of components are required to obtain a high reduction gear ratio and to adjust the optical axis of the focusing lens. A space for assembling these components is required, resulting in high manufacturing cost.
Some auto-focus cameras of this type adopt a structure wherein when a camera is rendered inoperative, an exposure window formed in the front surface of the lens barrel of a photographing lens is automatically covered by a barrier plate so as to protect an internal lens and a mechanism section. The conventional barrier plate is biased in an open direction in a plane perpendicular to the lens optical axis. More specifically, the barrier plate is assembled in the lens barrel of the photographing lens to be movable in the plane mentioned above while being biased in the open direction by a spring, and is forcibly closed by a retracting operation of the lens barrel of the photographing lens upon turning off of a main switch.
Therefore, in the conventional lens barrel of the photographing lens, a space for escaping the barrier plate when it is open must be formed in the radial direction of the photographing lens, and a mechanism for forcibly closing the barrier plate is assembled between a camera body and the lens barrel of the photographing lens. Therefore, the outer dimensions of the lens barrel of the photographing lens become large as compared with the diameter of the exposure window or the photographing lens. Thus, it is difficult to obtain a structure with a high product quality. In this structure of the lens barrel of the photographing lens, while the main switch is kept ON, since the barrier plate is kept open, the photographing lens cannot be satisfactorily protected. If the barrier plate is closed for some reason, an operator cannot know this. Thus, the operator away often perform a photographing operation in this state. In this structure, if the operator turns off the main switch without noticing that a foreign matter is jammed between the exposure window and the barrier plate, the moving mechanism of the barrier plate which is forcibly closed is excessively loaded, thus breaking the barrier plate.